The invention relates to methods and apparatus of operating devices (such as devices in wellbores) using actuators having expandable or contractable elements.
In a well, various devices may be activated to perform different tasks. Downhole devices may include valves (e.g., flow control valves or safety valves), perforating guns, and other completion components. Different forms of activation mechanisms, including hydraulic, mechanical, or electrical mechanisms, may be used. Mechanical activation typically involves lowering some type of setting or shifting tool to a desired depth to engage the downhole device to apply a force to move an actuator operably coupled to the downhole device. Hydraulic activation typically involves application of hydraulic pressure either through a tubing, a tubing-casing annulus, or a hydraulic control line to an actuator in a downhole device. Electrical activation typically involves communicating electrical power and/or signaling down an electrical cable, such as a wireline, an electrical control line, or other type of electrical line to a downhole actuator, which may include an electronic controller, a motor, or a solenoid actuator.
Conventional electrical actuators, such as solenoid actuators, typically require large amounts of electrical current to operate. Communication of high electrical currents may require relatively heavy electrical cables, which may be difficult to handle and which may take up too much space in a wellbore. Further, in some actuators, relatively sophisticated downhole electronic circuitry may be used. Such electronic circuitry may have reliability problems. Other types of actuators may also be associated with various issues. For example, mechanical actuators may be time-consuming and difficult to operate. Hydraulic and other fluid pressure actuators require a fluid pressure communications path, which may be impractical in certain parts of the wellbore. Also, leaks may develop that would render the hydraulic or other fluid pressure actuator inoperable.
A need thus continues to exist for improved actuators for operating downhole devices and other types of devices.